Electronic goniometer for radio direction finders



Sept.v28, 1948. J, H, NEwlTT I 2,450,014

ELECTRONIC GONIOMETER FOR RADIO DIRECTION FINDERS I Filed oct. 28, 1944 ssneets-sneet 2 2. 40cm/r may DOl/@LE 'OX/HL CWE 000815 Calif/4L @HELE J. H. Nr-:wrrT

Sept. 28, 1948.

ELECTRONIC GONIOMETER FOR RADIO DIRECTION FIHDERS Filed Oct. 28, 1944 E w# mi INVEN TOR. JD/l/V. H. #5W/TT f1 TTR/VEY Patented Sept. 28, i948 ELECTRGNIC GONIOMETER FORRADIO DIRECTION FINDERS IFolin H. Newitt, Montclair, N. J assignor toi Federal Telephone and Radio Corporation, New york, N. Y., a corporation of Delaware Application ctober 28, 1944,-Serial No. 560,823 13 Claims. (Cl. 343-121) This invention relates to new and useful lmprovements in goniometers and more particularly in goniometers co-operating withinstantaneous direction indicators.

The main object of the invention is to maintain .of the goniometer. The oscillator should be adjusted to produce triangular or other saw-tooth wave forms for controlling frequencyand phase synchronism.

These and other features of the invention will more clearly appear from the appended claims and the following detailed description of an embodiment illustrated in the drawings in which: Fig. 1 is a complete block diagram of the indicator equipment, electroni-c goniometer. equipment, and antenna array connected in accord-f ance with this invention;

Fig. 2 is a diagram of the gonimeter equipment and indicator equipment in block form,

and an antenna array for use therewith in schematic form;

Figs. 3 and 4 are circuit diagrams of the electronic goniometer; Figs. 3a and 3b are diagrams explaining the functioning of the circuit of Fig.-

3, and- Fig. 5 is a graph of a typical modulation schedule.

The electronic indicator as included in the block diagram of Fig. 1 comprises an oscillator l. a synchronizing voltage .source 2, an audio ampliiier 3, a phase shifter 4, two D. C. amplifiers 5 and 6, and a cathode ray tube 8. The oscillator l produces in its output a sine wave of high precision in either of the following two ways:

- (a) The oscillator may be of the phase shift type provided with a filter to produce substantiallly pure sine wave. Such van oscillator however cannot be synchronized from an outside source and could be used only where synchronism of the indicator is not needed.

(b) Where several indicators must be simultaneously operated, or where. for other reasons synchronism is desired, the oscillator should'be one adapted to produce triangular or other sawtooth wave forms and connected with an external A90",phase quadrature to one another.

2 synchronizing source 2. Thesaw-tooth wave may be sent through a filter to produce a substantially pure sine wave.

A triangular type of saw-tooth wave is recommended slnce it is the easiest of the saw-tooth waves to filter. A transitron oscillator'circuit, a negative resistive arrangement as described for example in Radio Engineers Handbook (F. E. Term'an, first edition, 5th impression, pages 318- 319), and in the .Funda-mentals of Vacuum Tubes, by A. V. Eastman (second edition, 7th impression, pages 432-433) with a large value of capacity in its 4output can be made to produce a suitable triangular wave form when properly adjusted. Synchron-ism may be obtained by insertion of synchronizing signal on the oscillator control grid. However, any suitable method may be used to obtain the desired sine wave form.

'I'he sine wave output of oscillator I is fed to an audio frequency amplifier 3 and then in one 'channel over a 90 phase shifter 4 to a D. C.

ampliier', and in a second channel directly to a D. C. amplier 6. These two channels are in put of ampliiier 5 is connected to the horizontal and the output of. 6 Iis' connected to the vertical deection plates of Ia. cathode ray tube, an end view of which is indicated at 8.

When two sine wave voltages of 90 phase quadrature, but` having the same frequency and amplitude are impressed on opposite plates of a cathode ray tube, the spot formed on the screen by the electron stream will describe a circle. The frequency of the circle will be equal to the frequency of the oscillator voltage producing it. Thus,.a 30 cycles per second sine wave would causethe cathode ray tube spot to describe thirty complete circles each second.

The amplitude of the` sine lwaves impressed on Fig. 2, is used to bias 'the D. C. amplifiers to plate current cut-01T condition, then the presence of -a null lwould remove this bias and allow the circle to expand to its maximum diameter.

As well known, in mechanical goniometer .sys-

tems for direction finding nulls are periodically produced bythe continuous rotation of a rotor. In the bearing indicator of such system the circle will be pulled inward at every point, except where the null occurs. This gives a directional indi- The outcation because a. sharp figure-ofeight pattern is produced by the spot of the indicator. Two reciprocal nu'ils occur during each electrical cycle,

The circle 'frequency is constant and the position of the nulls in relation to any point on the circumference of the circle changes with a change in direction of the received energy due to a redistribution of energy in the two sections of the antenna system. In other words, the goniometer balancesfor a null condition at different points during its rotation for different distribu- Ations of energy in the two'sections of the antenna array. The nulls will move in relation to a point on the cincle circumference in response to changes in antenna energy distribution caused bya change in direction of the received energy. The movement can be read on a calibrated scale located at the periphery of the circle.

The output of the electronic goniometer I3 (Figs. 1, 2 4and 3) of the present invention is fed to the signal receiver 1. The device I3 electronically simulates the rotary action of the customary mechanicall goniometer by the expedient of varying the gain of two pairs of electronic tubes Il, I5 and I6, I1 (Fig. 3) in a sine and cosine manner. The 'electronic goniometer I3 and an Adcock antenna array, I3a are included in Fig. 1 in block form to complete a direction indicating arrangement. This is accomplished by applying from a modulating signal source M (Figs. 1 and 2) slnusoidallly varying voltages at M1 to the plates of the linearly responsive tubes I6 and I1, and at M2 to the plates of I4 and I5. The stability and linearity of the device are greatly improved by using plate modulation with A. C. only, rather than by the alternative method of superimposing an A. C. voltage on a grid bias voltage and applying D .0. to the plates.

Triode curves show the greatest Ep-Ip linearity' close to zero bias and the goniometer is operated close to this point at all times. The goniometer makes use of a balanced input system comprising double coaxial cables I8, I9 whereby conventional directional arrays 20, 2| (such as an Adcock or crossed loops) may be used. Each section. of the antenna array is fed into a pair of said tubes, I6, I1 and I4, I5, respectively. The inputs of each tube pair are cross connected over resistances R5, Rg and R1, Rs, respectively, between the grid and the cathode o1' the pair. The purpose of this is to operate only one tube of a. pair at any one time since A, C. is applied Vto the plates over terminals M1 and M2, tubes of each pair are 180 out of phase, While the pairs are 90 out of phase in respect to each other.

With such a cross connection arrangement, the

, voltages on transmission lines I8 and I9 are always impressed between grid and cathode of an active tube. If such a cross connection were not made, the active tube would receive only the volt- Athus do not appreciably contribute to signal at-v tenuatlon by voltage division.

The voltages of the transmission lines I8 and i5 appear. across resistance R connected to the outputs of the tubes over output coupling con- -denser C1, C2, Cs, and C1.

The amplitude and phase relations are determined by the modulation schedule applied to the plates of the goniometer tubes. For example, as graphically shown in Fig, 5, when the modulating voltage is applied to tubes I6 and I1, it will rise from zero to maximum amplitude then drop back to zero, its 'phase will then reverse as it progresses again to a maximum and a minimum, completing the modulation cycle. The radio frequency phase reverses as first one tube and then the other of a pair becomes conductive. This phase reversal is necessary because when a target transmitter circumnavigates a directional system, such as an Adcock, only one section of the array reverses its phase when each quadrant is passed. Thus, ifl the phase of the other section were not reversed, voltages would be added instead oi' cancelled at points when nulls should occur.

The tubes of each pair are operated 180 out of phase in respect to each other, and one pair is operated out. of phase with the' other. It is easy to tell at any point on the modulation schedule of Fig. 5 which tubes are conducting and at what gain. From this information and from the phase relations of the input lines I8 and I9, the occurrence'of nulls may be determined. The following is the conduction schedule:

Degree of Cycle Col'ildllllling Let us assume a condition where the target transmitter is due north of the array (45 to the plane of both array sections 20, 2|). Since the amplitude of the voltage induced in either section of the directional array is directly proportional to the cosine of the angle formed by the plane of the arriving wave' front, and since the plane of the antenna pair is cut by thel Wave, the voltages would be .707 of their maximum possible value. However, each section of the array isintersected at 45 by the wave arriving from the north and,'therefore, the samevoltages will be obtained from each section of the array, the planes of the two sections of the array intersecting each other at a 90 angle. Thus, in the case of target transmitter north, and E1=Ez, i. e. the potentials a-pplied over I8 and I8 are the same, we can derive the following information from 'the modulation schedule of Fig..5:

Modulating conduct E o Outglgrg ing Tube put Reason 14 it Re .l

er le l0 0 El ac'ossR. 2 (p ,across R) 16, 15 0 l6i=l15E1Es (phases canceling n o 15 0 E; across R. 225 15, 17 0 151317. E1=E1 (in parallel across 21o: 11 o E, ac'ross R. 316 17, 14 0 17-14, EFE; (phases canceling o in R). 360 14 0 E; across R.

The foregoing shows how nulls occur for one case over the modulation schedule and illustrates that with the conditions as given, two nulls would occur 180 apart; at 135 and 315.

For other positions of the target transmitter,

the point at which nulls should occur may be determined from the fact that for north the nulls are 135 and 315. Actu-al null occurrence may be checked by referring to the modulation scheduie and schematic. It will be found that:

Reciprocal relations hold for the other major positions around the array.

While the foregoing spot-checks quite clearly illustrate'the operation of the goniometer, checks on a few intermediate points will be given. Where the target transmitter is NNE:

En-Cos 22.5=.924 Ei-Cos 67.5=.382

One null for NNE should be 112.5 since NE is 90 and 270 and N is 135 and 315.

Th'en at 112.5: y

Tube I5 conducts at .328 and I6 at .924. A null occurs since: E216G=E115G (the voltages cancel in R), where 16e and 15G are gains oftubes I6 and i5.

The phase and amplitude of the transmission line voltages E1 and E: are thus compared in the output resistor R.V For any value of phase and/or amplitude of E1 and En there is a point on the modulation schedule which will produce a null as the resultants of these voltages appear in the output resistor R. f

A few examples of theoretical conditions will be given to illustrate the action more fully. It is important that the device be in balance when no modulating voltages are applied. With no power applied to the goniometer and with Ei and Ez present in any values up to 100,000 microvolts, no noticeable voltage will appear across R, using a sensitive receiver of a few nv. sensitivity. This is so because C1=Cs and C2=C4 within a fraction of one percent. The internal capacities oi the tubes are closely equal and are very small percentages of their output coupling capacities.

When no power is applied to the goniometer, the resistor R is connected between the center tap of the capacitative voltage division system and a parallel resistive voltage division system.

This is best shown in Figs. 3a and 3b in which the same reference numerals are employed as in Fig. 3 except that CM to CH indicate the interternal capacitances of the tubesl to I1. The capacitative voltage division system is composed oft-Cil, Cl, C3, and Cl 6 in one section of the goniometer, and C2, C4, CM, and CIB in the other section of the goniometer. The parallel resistive voltage division system of one lsection comprises R and R2, and in the other section R3 and R4.

When no potential difference exists between the center taps of the two systems, i. e. resistive capacitive systems, no potentialexists across resistor R. When either tube of a pair becomes active upon the application of power to its plate circuit, the capacitative system becomes unbalanced inrespect to the resistive system and the unbalancepotential will develop across resistor R.

Reversing one set of transmission lines i8, I9

leading from the directional arrays 20, 2i causes the indicator pattern to shift Reversing the phase of Mr, or Ma (modulation schedule change) likewise causes the pattern to shift 904 for a given connection of the transmission lines to the input of the goniometer.

This feature may serve to allow for the provision of a sense system for the goniometer by using a sensing antenna and suitablyshifting the phase of either modulation voltage Mi or M2.

The cross connected input circuits necessitate to use chokes Li-Ls (Fig. 4) in the'lament circuits to counteract the high capacity between the laments and cathodes. Each iilament is directly groundedover one choke La. L4. Le and La. and is grounded also over iament by pass capacitor Cia through chokes Li. La. Le and L1.

The plate circuits have decoupling resistors RIS-i8 grounded over condensers Cs-Cl2 to exclude R. F. from the modulator circuits.

A coaxial connection 22 is provided between the goniometer i3 and the signal receiver 1. With cables having a high balance ratio at the desired frequency, this cable may be made indenitely long when terminated in its characteristic impedance.

The grid-cathode resistors Ri, Rz, R3 and R4 t Re, Rio,

serve to produce the necessary bias. and Rn and R12 are plate load resistors.

The accuracy of the device depends mainly upon the maintenance of sine wave yiorm modulation at a high degree of accuracy, the maintenance of a constant (90) phase relation between the two modulating voltages. and the maintenance of a linear relationship between gain and plate potentials in the goniometer tubes.

What is claimed is:

1. In combination, an electronic goniometer divided into two sections comprising electric dis charge devices, a directional antenna connected with each section, a source of sinusoidally varying modulating voltages applied out of phase to the two sections, an output load in which the phase and amplitude of the signals applied to the two sections is' compared, and an indicator comprising a sine wave generator controlling said source of modulatingl voltages.

2. In combinationI an electronic goniometer comprising two pairs of tubes. each having cathode, grid and anode electrodes, a directional antenna connected with the grids of each pair of tubes. a source of'sinusoidally varying modulating voltages. connections from said source to apply said voltages to the plates of each pair of tubes out of phase with respect, to 'one another, and to one pair 90 out of phase with respect to the other pair, a connection from the cathode of one tube to the grid of its pair to permit operation of only one tube of a pair at a time, a resistance connected in multiple to the plates of the four tubes, a radio receiver connected to the last mentioned resistance, and an indicator comprising a sine wave generator controlling said source of modulating voltages.

3. In combination, an electronic goniometer comprising two pairs or linearly responsive tubes, each-having cathode, grid and anode electrodes, a directional antenna system for each pair of tubes. balanced transmission lines connecting each system with the grids of its pair of tubes, resistance terminations for said lines having such low values that the grid resistance of one tube serves as the cathode resistance of its pair, a

Ysource of sinusoidally varying modulating voltages, connections from said source to apply said voltages to the plates of each pair of tubes 180 out of phase with respect to one another, and to one pair 90 out of phase with respect to the other pair, a connection including a resistance from the cathode of one tube to the grid of its pair to permit operation of only one tube of a pair at a time and insure a shift bias and prevent the flow of gridV current in the active tube, an output coupling condenser connected with the anode of each tube, a grounded resistance connected in multiple between the four output coupling condensers constituting a capacitative voltage division system, a radio receiver, a connection from said receiver to the last mentioned resistance shielded against direct pick-up of signals from sources other than from said grounded resistance, and an indicator comprising a sine wave generator controlling said source of modulating voltages.

4. In combination, `an electronic goniometer comprising two pairs of tubes, each having cathode, grid and anode electrodes, a directional antenna connected with the grids of each pair of tubes, a source of sinusoidally varying modulating voltages, connections from said source to apply said voltages to the plates of each pair of tubes 180 out of phase with respect to one another, and to one pair 90 out of phase with respect to the other pair, a connection Vfrom the cathode of one tube to the grid of its pair to permit operation of only one tube of a pair at a time, a resistance connected in multiple to the plates of the four tubes, a radio receiver connected to the last mentioned resistance. an electronic 'indicator comprising an oscillator to produce a. sine wave connected with said source of modulating voltages, two direct current amplifiers connected 90 quadrature to the oscillator, a cathode ray tube having vertical and horizontal deiiecting means,

connections from the output of each direct current amplifier to one of said deilecting means, and means for applying biasing voltages from output of said receiver to the direct current ampliers.

5. In combination, an electronic goniometer comprising two pairs of linearly responsive tubes, each having cathode, grid and anode electrodes, a directional antenna system for each pair of tubes, balanced transmission lines connecting cach system with the grids of its pair ottubes,

resistance terminations for said lines having such low values that the grid resistance of one tube serves as the cathode resistance of its pair, a source of sinusoidally varying modulating voltages, connections from said source to apply said voltages to the plates of each pair of tubes 180 out of phase with respect to one another, and to one pair. of 90 out of phase with respect to the other pair, Ia connection including a resistance from the cathode of one tube to the grid of its pair to permit operation of only one tube of a pair at a time and insure a shift bia-s and prevent the flow of grid current in the active tube, an output coupling condenser connected with the anode of each tube, a grounded resistance connected in multiple between the four output coupling condensers constituting a capacitative voltage division system, a radio receiver, a connection from said receiver -to the last mentioned resistance shielded against pick-up of signals from sources other than said grounded resistance, an electronic indicator comprising an oscillator to produce a sine Wave, an audio frequency amplifier connected with the output of said oscillator, a connection over which said amplifier controls said sourceof modulating voltages, a first and a second direct current amplifier, connections from the audio amplifier output to the direct current amplifiers, a phase shifter in one of the last mentioned connections to maintain them in quadrature to one another, a cathode ray tube having vertical and horizontal deflecting means, connections from the output of one direct current amplifier to one defiecting means and from the other direct current amplifier to the other reiiecting means, and means for applying biasing voltages from the output of said receiver to the direct current amplifiers to bias them to plate current cut-oi! conditions.

' 6', A goniometer having two electronic sections, said sections having multi-electrode discharge devices, an antenna'connected with each section, a source of alternating vcurrent modulating voltage applied out of phase to the two sections, and means for maintaining a linear relationship between'the gain and the modulat ing potentials of the two sections.

'7. A goniometer having two electronic sections,

each section having a pair of discharge devices, an antenna connected with each pair, a source of sine wave moduating voltage applied 90 out of phase to the two sections, and means for maintaining a linear relationship between the gain and the modulating potentials of the two pairs of devices.

8. A goniometer having two electronic sections. each section having a pair of multi-electrode discharge devices, two antennas, a balanced input from each antenna to a'section periodically to produce nulls therein and to vary the gain of said devices, a source of sine wave modulating voltage applied 90 out of phase to the two sections, means for maintaining alinear relationship between the gain and the modulating potentials of the two systems, and a resistor in which the phase and amplitude of the input voltages of the two systems are compared.

9. An electronic bearing indicator comprising an oscillator to produce a sine wave, an audio frequency amplifier, connected with the output of said oscillator, a first and a second direct current amplifier, connections from the audio amplifier output to said direct current amplifiers, a phase shifter in one of said connections to maintain them in 90 quadrature to one another, a cathode ray tube having vertical and horizontal deiiecting means, connections from the output of one direct current amplier to one deilecting means and from the other direct current amplifier to the other deiiecting means, a radio frequency signal receiver, and means for applying biasing voltages from the output of said receiver to the direct current amplifiers to bias them to plate current cut-of! condition.

10. An electronic goniometer comprising two pairs of multi-electrode tubes, a directional antenna connected with a rst electrode of each pair of tubes, a source of modulating voltages connected with a second electrode of each pair of tubes out of phase with respect to each other, and to one pair out of phase with respect to the other pair of tubes, connections between the rst and a third electrodes of each pair of tubes to permit operation of only one tube of a pair at a time, and an output load connected in multiple to the second electrodes of thetwo pairs of tubes.

11. An electronic goniometer comprising two pairs of multi-electrode tubes, a directional antenna connected with a first electrode of each pair of tubes, an alternating current source ot modulating voltages connected with a second electrode of each pair of tubes out of phase with respect to each other, and to one pair out of phase with respect to the other pair oi' tubes, connections between the rst and a third electrode of each pair of tubes to permit operation of only one tube of a pair at a time, an output load connected in multiple to the second electrode of the two pairs of tubes, and an indicator controlled by the goniometer for controlling said source.

12. An electronic goniometer comprising two pairs of linearly responsive tubes,- each having cathode, grid and anode electrodes, a directional antenna for each pair of tubes, balanced transmission lines connecting each system with the grids of its pair, a source of sinusoidally varying voltages, connections from said source to apply said voltages to the plates of each pair of tubes 180 out of phase with respect to one another, and to one pair 90 out of phase with respect to the' other pair. a connection from. the cathode of one tube to the grid of its pair to permit operation of only one tube of a pair at a time, an output coupling condenser connected with each plate, anda resistance connected in multiple to the four output coupling condensers.

13. An electronic goniometer comprising two pairs of linearly responsive tubes. each having cathode, grid and anode electrodes, a directional antenna system for each pair of tubes, balanced transmission lines connecting each system with the grids of its pair, resistance terminations for said lines having such low values that the grid resistance on one tube serves as the cathode resistance of its pair, a source of sinusoidally varying voltages, connections from said source to apply said voltages to the plates oi each pair of tubes 180 out ot phase with respect to one another, and to one pair out of phase Jwith respect to the other pair, a connection including` a resistance from the cathode of one tube to the grid of its pair to permit operation o! only one tube of a. pair at a time by insuring a shiit bias -and preventing the ilow of grid current in the active tube, an output coupling condenser connected with each plate, and a resistance connected in multiple to the four output couplinz condensers.

JOHN H. NEWITT.

REFERENCES CITED The following references are of record in the i'lle of this patent:

' UNITED STATES PATENTS Number Name Date 2,156,297 Kruesi May 2, 1939 2,174,016 Sullinger Sept. 26, 1939 2,184,306 Kruesi Dec. 26, 1939 2,208,378 Luck July 16, 1940 2,213,273 Earp Sept. 3, 1940- 2,279,021 Cooper etal. Apr. 7, 1942 2,408,039 y Busignles Sept. 24, 1946 FOREIGN PATENTS Number Country y Date i 526,658 i Great Britain Sept. 23, 1940 

